The present invention relates to novel compounds that are particularly useful in marine antifoulant coating compositions.
Marine fouling on ships and marine structures has been a problem for thousands of years. This problem has been recently addressed primarily by the use of certain coatings containing biocides that are toxic to marine organisms. These conventional coatings leached biocides out of the coating when in seawater.
Such a paint system, however, fails to provide a desired constant toxicant release, and moreover, does not advantageously erode in service. This is due to the selective extraction of the water-soluble component and consequent leaching of the toxicant from the interior of the paint film. A matrix of the insoluble resin component remains behind after the water-soluble component of the film (gum rosin) is leached away. Moreover, the spent paint film no longer controls fouling even though it might contain up to 30-40% of the initial level of toxicant because water penetration required for leaching the toxicant to the surface is limited through the matrix of residual resin. Spent antifouling systems of this type do not provide a suitable base for repainting since they possess poor mechanical properties due to the voids in the film resulting in poor adhesion of the new paint film.
Attempts to incorporate toxicants into water soluble polymers and to use these as antifouling paints have also failed to produce the desired results. Such paints swell in seawater and cannot be expected to provide good mechanical properties and uniform control of fouling since the whole paint film is weakened on prolonged water immersion.
In recent years, so-called self-polishing antifouling coatings have become increasingly popular. These coatings are based on polymers of tributyltin methacrylate, methyl methacrylate, and film softening monomers such as 2-ethylhexyl acrylate. The organotin polymer acts as the paint binder. All such paints also contain a toxicant additive such as cuprous oxide or a triorganotin compound. In addition, the usual paint additives such as pigments, thixotropic agents, etc. may also be present. In normally alkaline seawater, the polymeric organotin binder is gradually hydrolyzed and the tributyltin is liberated in a form that is an active antifoulant. The hydrolyzed polymer formed is water-soluble or water-swellable and is easily eroded off the surface by moving seawater, exposing a fresh surface of paint. The major advantage of these systems is that, unlike leaching paints, toxicant release is linear with time and all of the toxicant present is utilized over the lifetime of the paint. Furthermore, there is no need to remove the residues of an old self-polishing paint system prior to repainting, since the composition of the residue is essentially the same as it was when originally applied unlike conventional antifouling paints which leave a weak, leached-out matrix of binder on the ships' hull at the end of their lifetime. An additional advantage claimed for such systems is a reduction in hull surface roughness with time as a consequence of erosion of the paint film. This roughness reduction translates to fuel savings for the ship operator.
Sea-going vessels usually have between 2 and 4 coats of antifouling paint, each coat of 100 microns film thickness, applied to the hull. This coating, of 200 to 400 microns total film thickness, is expected to last for about five years.
A marine antifoulant coating should preferably meet some criteria in order to be commercially acceptable, such as:
1. The polymer is preferably soluble in a paint media for easy application; PA1 2. The polymer solution preferably has good film-forming properties; PA1 3. The film coating preferably has good adhesion to the ship's surface and is flexible; PA1 4. The film preferably undergoes hydrolysis only at the coating surface. This permits the controlled release of the metal. The remaining paint surface becomes susceptible to the moving seawater and is eroded. This mechanism is known as "self-polishing" and a marked improvement in the ship's fuel efficiency is observed; and PA1 5. The polymer preferably has controlled release characteristics. PA1 where M is a Group 3 element, which includes Sc and Y, PA1 where M is a Group 4 element, PA1 where M is a Group 5 element, PA1 where M is a Group 7 element, which includes Mn, Re, and Tc, PA1 where M is a Group 8 element, PA1 where M is a Group 9 element, PA1 M has a coordination number of 4, 5, or 6; and PA1 M has mainly oxidation states of +1, +2, +3, or +4. PA1 where M is a Group 10 element, PA1 where M is a Group 11 element, PA1 where M is a Group 12 element, PA1 where M is a Group 13 metal element, which includes Al, Ga, In, and Tl, PA1 where M is a Group 14 metal element, which includes Si, Ge, Sn, and Pb, PA1 where M is a Group 15 metal element which includes As, Sb, and Bi, PA1 where M is a Group 16 metal element, which includes Te and Po, PA1 R.sup.1 is a polymerizable group. In other words, R.sup.1 will be a substituent which will be polymerizable when the compound of formula (I) is polymerized into a polymer. For purposes of the present invention, R.sup.1 can be any type of polymerizable group. This includes: PA1 H.sub.2 N--R.sup.8 --NH.sub.2 PA1 HO.sub.2 C--R.sup.9 --CO.sub.2 H PA1 H.sub.2 N--R.sup.10 --CO.sub.2 H PA1 HO--R.sup.11 --OH PA1 Cl--R.sup.12 --Cl PA1 ClOC--R.sup.13 --COCl PA1 1. The polymer is solvent soluble, for easy application. PA1 2. The polymer solution provides a clear, hard film with enough flexibility to coat a ship's surface. PA1 3. The film undergoes at least some surface hydrolysis to release a metal, to become a material that either dissolves or swells and is attritted or dissolved off to provide a fresh and new polymer layer that is preferably smooth to preserve a ship's fuel efficiency.
Accordingly, the present invention is directed to novel compounds and marine antifoulant coating compositions containing polymers polymerized from these compounds.
Additional features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention. The objectives and other advantages of the present invention will be realized and attained by means of the elements and combinations particularly pointed out in the written description and appended claims.